The fuel shortages, which have developed in recent years and the dependence on fuel from foreign sources, have necessitated the search for ways and means to save fuel. The present invention is directed to a novel and simple device to recover heat from chimney flue gases. It involves the use of a pair of coils, one in a chimney flue and one in a cold air flue to carry heat, otherwise lost out the chimney, to the air being heated by the furnace.